1. Field of the Invention
The present invention relates to the field of outdoor fluid transport systems, and in particular, to a removable, passive device which inhibits freezing of standing water contained within the fluid transport system.
2. Description of the Related Art
Municipal water supplies are generally protected from contamination by devices called backflow prevention devices. Backflow prevention devices are emplaced in a fluid transfer system to inhibit reversal of water flow back into the supply side. Flow reversal can potentially entrain contaminants picked up in the receiving side back into the supply of potable water, thereby contaminating the water supply.
Backflow prevention devices are typically required by municipal agencies and by code to be installed above ground in order to facilitate inspection and service of the devices. In addition, many backflow prevention device designs direct backflowing water out of the fluid transfer system and it is thereby desirable to elevate the backflow prevention device above the ground surface such that gravity draws away the discharged water so that the water and any entrained contaminants do not remain in proximity to the backflow prevention device and be possibly drawn back into the potable supply. The connecting plumbing is typically run underground for insulation, aesthetic, and protection purposes. As the devices are exposed to the ambient air, in many places they are also exposed to potentially sub-freezing temperatures.
Water expands in the phase change from liquid to solid and thus a solid object, filled with water, is exposed to high pressures and potential resultant damage as the water within freezes and expands. With regards to a solid backflow prevention device, the damage can be as little as a blown rubber seal or as major as a cracked bronze body. Seals can be replaced with a relatively simple tear down of the assembly. Broken bodies require complete replacement of the unit. A new unit typically requires testing and certification by a state licensed backflow technician. The average replacement cost of 1 to 2 inch sized backflow devices is between $300 and $800. As the water supply system and thus the backflow prevention devices supply water for businesses, manufacturing plants, irrigation systems, homes, schools, and many other facilities, it can be appreciated that water usage is nearly continuous and interruption of service cannot be tolerated.
In order for water contained with a fluid transport system to freeze, sufficient heat must be transferred out of the water to bring it below the freezing point. Heat transfer occurs via three mechanisms. A first mechanism is heat radiation wherein matter above absolute zero radiates thermal energy outwards. Heat radiation does not require a material medium through which to transfer the heat, i.e. radiation can occur through a vacuum, however, certain materials are quite effective at reflecting incident heat radiation back to the source material where it can be reabsorbed.
A second mechanism of heat transfer is heat conduction wherein the thermal energy of atomic motion is transferred directly through a material or from one material to another. Heat conduction requires material through which to transfer the heat and the heat will always flow from regions of higher temperatures to regions of lower temperatures according to well-known thermodynamic principles.
The third mechanism of heat transfer is heat convection wherein a temperature gradient induces fluid materials in the region of the gradient to establish a flow from the regions of higher temperature to regions of lower temperature. Convection is distinguished from conduction in that convection involves the actual movement of material while conduction is the transfer of the molecular heat energy alone.
Insulation involves inhibiting the transfer of heat through at least one and preferably all of the three mechanisms. In the field of the present invention, wherein the backflow devices are exposed to ambient air, typically at the temperate temperatures of xe2x88x9230 to 50xc2x0 C., radiation, conduction, and convection are all mechanisms of heat transfer. Insulating against radiation typically involves placing a material in close proximity to the device of interest which reflects incident heat radiated from the device back to the device. Conduction insulation typically involves surrounding the device with material that is a poor conductor of heat to thereby slow the conduction out of the device. Convective insulation inhibits fluid movement around the device of interest so that fluid surrounding the device can not readily carry heat away.
One generally accepted method for backflow freeze protection has been the wrapping of the backflow device in fiberglass insulation covered by layers of a vinyl self-adhesive tape. Fiberglass insulation manufacturers list the thickness of the batting, usually 6 to 13 inches, required to achieve the required insulation R-value. However, the wrapping of the fiberglass with the tape locally compresses the fiberglass at different points such that some of the insulation efficiency is lost. Another problem with fiberglass insulation is that the material looses much of its insulation ability if the material becomes saturated with water. The water displaces the air held within the fiberglass materials. Trapped air is a fairly effective conductive and convective insulator, whereas water is a relatively poor insulator. Since the backflow prevention devices are installed outdoors, any tears or gaps in the vinyl wrapping can allow water to enter the insulation. Backflow devices also often develop leaks or vent water during normal operation. The tight tape wrapping can actually trap this water and saturate the insulation.
Most municipal water agencies require that backflow devices be tested and re-certified annually. This requires the removal of all insulation materials from the backflow device assembly. The fiberglass and vinyl tape is typically cut away from the device and discarded. The device is then rewrapped once the testing is completed. Contractors generally charge between $80 and $120 to re-wrap a backflow device in the manner described above. Thus fiberglass wrapped with tape is not an optimal insulator and is relatively expensive to install and maintain.
An alternative type of insulation enclosure on the market is constructed of fiberglass resin and/or sheet aluminum. The enclosure is a solid box-like structure that totally encloses the backflow device. These enclosures are mounted on concrete pads and have built in hinges that allow for tilting of the enclosure to allow for access to the equipment. These devices usually offer a fairly low R-value as the enclosure traps a great deal of air between the equipment and the enclosure. The air is free to circulate within the enclosure and thus convect heat from the backflow prevention device and the water contained therein in the manner previously described.
An additional aspect of many of these enclosures is that they include active heating of the interior of the enclosure and/or the backflow prevention device. The heating is typically resistive electrical heating supplied via line supply. The electrical heating is effective at supplying sufficient heat to the backflow device to inhibit formation of ice within the device. However, it can be appreciated that supplying electricity to the heating elements is an ongoing expense throughout the use of the enclosure. In additional, installing the heating elements and supplying them with electricity is an added expense and difficulty in installing the enclosures. The devices are accordingly expensive to purchase and install and are not easily retrofitted onto existing backflow devices.
A third known method of insulating a backflow prevention device is to install a pre-made blanket type cover over a backflow device. The ornamental design of such a cover has been issued U.S. Design Pat. No, 349,754. This blanket uses common housing construction type fiberglass insulation sewn into a canvass bag. The encapsulation of the fiberglass in the canvass actually compresses the fiberglass batting to some degree thus reducing insulation efficiency. The design of this blanket also does not completely wrap the fiberglass batting around the sides of the backflow prevention unit. This exposes portions of the backflow device to the ambient air and thus associated conductive and convective heat loss. This is due to the compression of the fiberglass that is required by the sewing of the seams with insulation materials and canvass together. Thus the sides of the backflow prevention device are only covered by the canvass bag material and are not effectively insulated. The design also includes semicircular cut away portions at the two lower corners of the cover. These areas expose the piping of the backflow device assembly to the air. This further exposes the fluid transport system and the water in the system to the ambient air and the risk of freezing.
The blankets of this design are made with simple exterior stitching that can easily become frayed or damaged. The fiberglass batting inside is not a single piece but rather two strips that are not secured together to create a continuous insulation layer. This weakens the overall integrity of the blanket and increases the potential for damage to the blanket during use. The canvass materials are water repellent but tests have shown the material to be easily torn. Any tears can allow water to enter the insulation and reduce or eliminate the insulation ability in the manner previously described.
The use of fiberglass batting and a canvass enclosure also presents attractive nesting materials for rodent pests. Tears in the canvass fabric or holes chewed by rodents allow entry of the pests into the interior. Long term field reports on the blankets previously manufactured indicate that the waterproof coating applied to the canvass quickly becomes cracked with exposure to the sun and that this allows water to penetrate into the bags.
It can be seen from the foregoing that there is an ongoing need for an inexpensive, reusable insulative cover for backflow prevention devices and other exposed regions of fluid transport systems. The insulation should be effective enough to provide adequate resistance to freezing conditions without requiring active heating. The materials of the cover should be resistant to environmental conditions commonly found outdoors and should not comprise attractive nesting or food material to rodents, birds, insects, plants, or fingi. The construction and materials of the cover should be such that the covers are resistant to water penetration and, in case of such penetration, substantially retain their insulating capability. The covers should be inexpensive to produce and install and should be reusable. It would be an additional advantage for the covers to include a securing mechanism so that vandals, curious children, or animals could not readily remove the covers.
The aforementioned needs are satisfied by the present invention, which, in one aspect, is a device for thermally insulating regions of a fluid transport system. The device comprises a flexible outer cover, an insulative bag removably attached inside the outer cover such that the outer cover and insulative bag define an interior cavity, a sealing structure attached to the insulative bag and positioned so as to removably seal the interior cavity of the insulative bag about the fluid transport system, and a plurality of securing structures interconnecting the outer cover and the insulative bag so as to removably secure the device to the region of the fluid transport system. In one aspect, the interior cavity of the device closely conforms to the contour of the region of the fluid transport system to improve the insulative properties of the device.
In another aspect of the invention, the device includes at least one layer of radiant barrier material and at least one layer of air retaining material. In one alternative aspect, the radiant barrier material and air retaining material is placed in alternating layers.
In yet another aspect of the invention, the device is made of materials that are unattractive nesting or food materials to animals, birds, insects, plants, or fuigi. The materials also absorb less than 20% by weight of water and are resistant to exposure to sunlight and temperature extremes.
These and other objects and advantages will become more fully apparent from the following description taken in conjunction with the accompanying drawings.